Self-attaching fasteners are now used extensively in mass production applications by the automotive and appliance industries, for example, to permanently attach a structural element to a panel, such as a metal bracket, frame member or body panel. U.S. Pat. Nos. 2,707,322 and 3,648,747 disclose pierce nuts which have been widely accepted by the automotive industry, wherein the pierce nut is permanently attached to a metal panel in a die press, and the press may also be utilized to form the metal panel into a contoured shape. A pierce nut is permanently installed in the metal panel with each stroke of the press, wherein the pilot portion of the pierce nut pierces a slug from the panel and the panel is then deformed into grooves provided in the body portion of the nut. U.S. Pat. Nos. 4,555,838 and 4,610,072 disclose improved fastening systems for permanently installing male and female fasteners in a panel in mass production applications. A fastener in such fastening systems include a tubular or annular barrel portion which is riveted to the panel during the installation. The tubular barrel portion may be utilized to pierce a slug from the panel, which is received in the tubular barrel portion as disclosed in U.S. Pat. No. 4,555,838, or a punch may be utilized to pre-pierce or simultaneously pierce the panel as disclosed, for example, in U.S. Pat. Nos. 4,711,021, 4,831,698 and 4,713,872. In recent years, the automotive industry, for example, has substantially reduced the weight of vehicles to improve fuel efficiency and the thickness of the metal panels and plates utilized by this industry has also been reduced. These fastener systems were designed, in part, to attach a fastener to thinner panels, including steel panels having a thickness of about 0.030 inches.
There is a need, however, for a fastener system for heavier gauge panels and fastener systems having improved torque resistance. The fastener system disclosed in the above-referenced co-pending application may be utilized with a broader range of panel thicknesses, including steel panels ranging in thickness from 0.75 mm to 4 mm.
There is also a need for a fastener system which attaches a plurality of panels in face-to-face relation which has not been met by the fastener systems disclosed in the above-referenced patents. At present, steel panel assemblies are typically attached by spot welding. A weld fastener is attached to one of the panels, forming a fastener and panel assembly. For example, the axle housing of an automobile may be attached to a U-shaped frame assembly which comprises two nested steel panels which are spot welded together. Holes are formed in the panels where the fasteners are required to attach the axle assembly to the frame and the fasteners are welded to the inside panel aligned with the holes. The frame assembly may then be dip coated with wax to reduce corrosion; however, the liquid wax wicks between the panels because the panels are not in intimate contact. When bolts are threaded into the weld nuts attached to one of the panels, the panels are compressed and the wax is extruded from between the panels. However, because the wax is viscous, it is extruded slowly and the bolts must be tightened several times to ensure a tight connection. Further, the welded fasteners may also be subject to failure under high torque loads.
The fastener and panel assembly of this invention may be utilized to attach a plurality of panels in intimate matting face-to-face relation such that wax, for example, will not wick between the panels and the fastener provides improved torque resistance. Further, the fastener is self-piercing, such that the fastener may be utilized in mass production applications in a die press. The method of this invention may also be used to interconnect two or more panels together in a conventional die press and provides improved pull-out and push-through resistance. Thus, the fastener and panel assembly of this invention provides important advantages over the prior art and fulfills a need which is not met by the present fastener assemblies.